Two pixel electrodes interposing the signal line extending into without extending beyond the recess on the protection film caused by the contact hole

ABSTRACT

In an electrode substrate used in a liquid crystal display device, a contact hole for connecting a signal line to a drain electrode of a pixel thin film transistor is provided in a position overlapping a pixel electrode in order to improve yields by reducing a short circuit between adjacent pixel electrodes. With this configuration, the contact hole does not exist at a boundary between the two adjacent pixel electrodes. Accordingly, the pixel electrodes do not suffer an influence of an electrode material remaining at a recess of the contact hole, and a short circuit between the adjacent pixel electrodes can be thereby prevented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2003-38572 filed Feb. 17, 2003; theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode substrate for a displaydevice, more specifically, to a structure of an array substrate used inan active matrix liquid crystal display device.

2. Description of the Related Art

In recent years, active matrix liquid crystal display devices arebecoming mainstream in the field of flat display devices due to reasonsincluding high contrast with small crosstalk, capability of transmissivedisplay and large-screen display, and the like. A liquid crystal displaydevice known of this type is disclosed in Japanese Unexamined PatentPublication No. 2002-296619.

FIG. 1 is a plan view showing a schematic configuration of a pixel in aconventional liquid crystal display device. Meanwhile, FIG. 2 is across-sectional view taken along the I—I—I line in FIG. 1, and FIG. 3 isa cross-sectional view taken along the II—II line in FIG. 1.

The liquid crystal display device includes an array substrate 100 and acounter substrate 200 which are disposed to face each other, while aliquid crystal layer 300 is formed in a space between the bothsubstrates.

The array substrate 100 includes scan lines 102, auxiliary capacitorlines 130 disposed in planarly parallel to the scan lines 102 on thesame plane, and signal lines 101 disposed in planarly perpendicular tothe scan lines 102 and the auxiliary capacitor lines 130 through aninsulating film 160, all of which are formed on a glass substrate 105.

A pixel TFT 110 is formed at an intersection of the signal line 101 andthe scan line 102 as a pixel switching element. A protection film 170 isformed on a surface of this pixel TFT 110. Moreover, a color filter 180and a pixel electrode 120 are formed in a region surrounded by thesignal lines 101 and the auxiliary capacitor lines 130 (the regionindicated by bold lines in FIG. 1). The pixel TFT 110 includes asemiconductor layer 111, a gate electrode 112 connected to the scan line102, a drain electrode 113 connected to the signal line 101, and asource electrode 114 connected to the pixel electrode 120.

Here, reference numeral 140 in FIG. 2 denotes an outgoing lineconnecting the drain electrode 113 of the pixel TFT 110 and the pixelelectrode 120, reference numeral 150 denotes a gate insulating film, andreference numeral 190 denotes an alignment film formed on a surface ofthe pixel electrode 120. A polarizing plate 195 is attached to outsideof the glass substrate 105.

The counter substrate 200 includes a counter electrode 210 and analignment film 230 which are sequentially formed on a glass substrate220. Moreover, a polarizing plate 240 is attached to outside of theglass substrate 220.

As shown in FIG. 2 and FIG. 3, the signal line 101 for supplying a videosignal and the drain electrode 113 of the pixel TFT 110 are connected toeach other through a contact hole 115 which is provided so as topenetrate the insulating film 160 and the gate insulating film 150.Conventionally, the contact hole 115 has been disposed between adjacentpixel electrodes 120, and respective ends of the adjacent pixelelectrodes 120 have been separated by a constant dimension at apertureportions of the contact hole 115.

However, in the array substrate 100 of the above-describedconfiguration, a horizontal dimension A from a bottom of the contacthole 115 to the end of the pixel electrode 120 may become shorter than ahorizontal dimension B of a tapered portion of the contact hole 115because of manufacturing errors when forming the pixel electrode. Inthis case, an electrode material such as ITO tends to remain at recessedportions of the contact hole 115 indicated by arrows in FIG. 3 whenforming the pixel electrodes 120. Accordingly, there has been a risk ofa short circuit between the adjacent pixel electrodes 120 attributableto the remaining electrode material. When the adjacent pixel electrodes120 are short-circuited as described above, the pixels turn out to bedefective pixels because of incapability of retaining original writevoltages. Accordingly, such a short circuit would constitute a problemof reduction in yields.

An object of the present invention is to provide an electrode substratefor a display device which can achieve fabrication of liquid crystaldisplay devices at high yields by reducing short circuits betweenadjacent pixel electrodes.

SUMMARY OF THE INVENTION

An electrode substrate for a display device of the first inventioncomprises a plurality of scan lines and a plurality of signal lineswhich are disposed so as to intersect one another, a plurality of pixelelectrodes disposed at respective intersections, switching elementsprovided at the respective intersections, each of the switching elementsbeing configured to allow conduction between the signal line and thepixel electrode by an instruction of a gate signal to be supplied to thescan line and thereby to write a video signal supplied to the signalline into the pixel electrode, and contact holes provided in eachposition overlapping each of the pixel electrodes, each of the contactholes being configured to connect the signal line and one electrode ofthe switching element.

The second invention is a electrode substrate for a display devicewherein an end of one of the two pixel electrodes which are adjacent toeach other while interposing the signal line is provided in a positionoverlapping part of the contact hole, an end of the other one of the twopixel electrodes is distant from an aperture edge of the contact hole bya longer dimension than a horizontal dimension of a tapered portion ofthe contact hole.

An electrode substrate for a display device of the third inventioncomprises a plurality of scan lines and a plurality of signal lineswhich are disposed so as to intersect one another, a plurality of pixelelectrodes disposed at respective intersections, switching elementsprovided at the respective intersections, each of the switching elementsbeing configured to allow conduction between the signal line and thepixel electrode by an instruction of a gate signal to be supplied to thescan line and thereby to write a video signal supplied to the signalline into the pixel electrode, and contact holes provided in eachposition overlapping each of the signal lines, each of the contact holesbeing configured to connect the signal line and one electrode of theswitching element wherein respective ends of the two pixel electrodes,being adjacent to each other while interposing the signal line, aredistant from aperture edges of the contact holes severally by adimension longer than a horizontal dimension of a tapered portion of thecontact hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a schematic configuration of a pixel in aconventional liquid crystal display device.

FIG. 2 is a cross-sectional view showing the schematic configuration,which is taken along the I—I—I line in FIG. 1.

FIG. 3 is a cross-sectional view showing the schematic configuration,which is taken along the II—II line in FIG. 1.

FIG. 4 is a perspective assembly view showing a configuration of aliquid crystal display device according to a first embodiment.

FIG. 5 is a plan view showing a schematic configuration of an arraysubstrate according to the first embodiment.

FIG. 6 is a plan view showing a schematic configuration of each pixel inthe liquid crystal display device according to the first embodiment.

FIG. 7 is a cross-sectional view showing the schematic configuration,which is taken along the III—III line in FIG. 6.

FIG. 8 is a plan view showing a schematic configuration of each pixel ina liquid crystal display device according to a second embodiment.

FIG. 9 is a cross-sectional view showing the schematic configuration,which is taken along the IV—IV line in FIG. 8.

FIG. 10 is a plan view showing a schematic configuration of each pixelin a liquid crystal display device according to a third embodiment.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

Now, description will be made on a case of applying an electrodesubstrate according to a first embodiment to a liquid crystal displaydevice. Here, in the respective drawings, elements equivalent to thoseillustrated in FIG. 1 to FIG. 3 are denoted by the same referencenumerals.

As shown in FIG. 4, this liquid crystal display device adopts aconfiguration in which an array substrate 100 and a counter substrate200 are disposed opposite to each other, peripheries of the bothsubstrates are sealed with a sealing member 400, and a liquid crystallayer is formed in a space between the array substrate 100 and thecounter substrate 200 by filling a liquid crystal material therein froman inlet formed on the sealing member 400. In this embodiment, the arraysubstrate 100 corresponds to the electrode substrate.

As shown in FIG. 5, on the array substrate 100, there are formed a pixelarea 196 constituting a display region, an OLB pad 197 for inputtingvideo signals, control signals, and the like from outside, an X driver(a signal line drive circuit) 198 for supplying the video signals tosignal lines 101, and a Y driver (a scan line drive circuit) 199 forsupplying gate signals to scan lines 102.

A plurality of signal lines 101 and a plurality of scan lines 102 arearranged in a matrix fashion in the pixel area 196 so as to intersectone another, and auxiliary capacitor lines 130 are arranged in parallelto the scan lines 102. Moreover, a pixel TFT 110 as a switching element,and a pixel electrode 120 corresponding to the pixel TFT 110 aredisposed on each intersection. An area surrounded by broken lines inFIG. 5 corresponds to one pixel. Note that FIG. 5 illustrates only onesignal line 101 and one scan line 102 for convenience.

A gate electrode 112 which is a control electrode of the pixel TFT 110is connected to scan line 102 in each row, and a drain electrode 113which is one of main electrodes is connected to the signal line 101 ineach column. Moreover, a source electrode 114 which is the other mainelectrode is connected to the pixel electrode 120 and an auxiliarycapacitor element 131. The auxiliary capacitor element 131 forms anauxiliary capacitor (Cs) between the pixel electrode 120 and theauxiliary capacitor line 130. Moreover, a given auxiliary capacitorvoltage is supplied from an unillustrated external circuit to theauxiliary capacitor line 130.

In the meantime, a counter electrode which is electrically opposed tothe pixel electrode 120 is disposed on the counter substrate 200 side. Acounter voltage is supplied from an unillustrated external circuit tothis counter electrode.

Here, switching elements of the pixel TFTs 110, of the X driver 198, andof the Y driver 199 are made of polysilicon TFTs which are formed on thearray substrate 100 in the same process.

Next a structure of a pixel on the array substrate 100 of theabove-described configuration will be described. As shown in FIG. 6, inthis embodiment, a contact hole 115 for connecting the signal line 101and the drain electrode 113 of the pixel TFT 110 is provided in aposition overlapping a pixel electrode 120 a.

To be more precise, as shown in FIG. 7, the contact hole 115 is providedso as to penetrate an insulating film 160 and a gate insulating film150, and the signal line 101 is connected to the drain electrode 113through this contact hole 115. The signal line 101 is recessed at aportion corresponding to the contact hole 115.

A protection film 170 is formed on the signal line 101, and a colorfilter 180 is formed thereon. The pixel electrode 120 a is formed on thecolor filter 180 so as to overlap the position recessed by the contacthole 115.

A space between the pixel electrode 120 a and a pixel electrode 120 b isseparated by a given dimension at a flat portion on the color filter180. Note that the two adjacent pixel electrodes 120 disposed on bothsides of the signal line 101 are denoted as the pixel electrodes 120 aand 120 b for convenience of explanation.

Next, an operation of this liquid crystal display device will be brieflydescribed. When the gate signal is supplied from the Y driver 199 toeach of the scan lines 102, the pixel TFT 110 connected to the relevantscan line 102 is turned on and the source and drain thereof areconducted so as to allow writing of the video signal. When the videosignal is supplied from the X driver 198 to each of the signal lines 101synchronously with the gate signal, the video signal is written in thepixel electrode 120 at the timing when the source and drain of the pixelTFT 110 are conducted. This video signal is retained between the pixelelectrode 120 and the counter electrode 210 as a signal voltage. Duringthis period, a liquid crystal layer 300 reacts in response to themagnitude of the signal voltage, and an amount of transmission ofunillustrated backlight is controlled for each pixel. Such an operationis executed for all the pixels within one-frame period, and atransmitted image for one screen shot is thereby displayed.

Therefore, according to this embodiment, the contact hole 115 does notexist at a boundary between the adjacent pixel electrodes 120 a and 120b, and respective ends 121 a and 121 b of the pixel electrodes 120 a and120 b are formed separately at the flat portions of the color filters180 with a given dimension. In this way, even if the positions of thepixel electrodes 120 are shifted due to manufacturing errors whenforming the pixel electrodes, it is possible to prevent the adjacentpixel electrodes from constituting a short circuit attributable to anelectrode material remaining at the recess of the contract hole 115.

Second Embodiment

As shown in FIG. 8, in this embodiment, part of the contact hole 115 isdisposed so as to overlap the end of the pixel electrode 120 a. FIG. 9shows an example of forming the end 121 a of the pixel electrode 120 aso as to reach a bottom of the recess of the contact hole 115. However,it is also possible to form the end 121 a of the pixel electrode 120 aso as to reach a tapered portion. In the meantime, assuming a horizontaldimension of the tapered portion of the contact hole 115 as C, the end121 b of the adjacent pixel electrode 120 b is formed in a position awayfrom an aperture edge of the contact hole 115 by a dimension D, which isnot less than the dimension C. For the rest, elements equivalent tothose illustrated in FIG. 6 and FIG. 7 are denoted by the same referencenumerals and duplicate explanations will be omitted herein.

According to this embodiment, the end 121 a of the pixel electrode 120 ais disposed in the position overlapping part of the contact hole 115,and the end 121 b of the pixel electrode 120 b is formed in the positionwhich is distant from the aperture edge of the contact hole 115 by thedimension D. In this way, even if the positions of the pixel electrodes120 are shifted due to manufacturing errors when forming the pixelelectrodes, it is possible to prevent the respective ends 121 a and 121b of the adjacent pixel electrodes 120 a and 120 b from constituting ashort circuit attributable to an electrode material remaining at thebottom of the contract hole 115.

Moreover, according to the present invention, the contact hole 115 isdisposed in the position shifted to the signal line 101 side as comparedto FIG. 6. Therefore, it is possible to increase an aperture ratio ofthe pixel electrode 120 a more than the first embodiment.

Third Embodiment

As shown in FIG. 10, in this embodiment, the contact hole 115 isdisposed in the position overlapping the signal line 101 as similar toFIG. 1. Moreover, respective ends 121 a′ and 121 b′ of the pixelelectrodes 120 a and 120 b, which are adjacent to each other whileinterposing the signal line 101, are formed in positions distant fromthe aperture edges of the contact hole 115 by the dimension D (>C).Here, although the dimensions D and C are not indicated in FIG. 10,these dimensions refers to the same dimensions described in the secondembodiment by use of FIG. 9. For the rest, elements equivalent to thoseillustrated in FIG. 6 are denoted by the same reference numerals andduplicate explanations will be omitted herein.

According to this embodiment, although the contact hole 115 is formed inthe position overlapping the signal line 101, the respective ends 121 a′and 121 b′ of the adjacent pixel electrodes 120 a and 120 b are formedin the positions distant from the aperture edges of the contact hole 115by the dimension D. In this way, even if the positions of the pixelelectrodes 120 are shifted due to manufacturing errors when forming thepixel electrodes, it is possible to prevent the respective ends 121 a′and 121 b′ of the adjacent pixel electrodes 120 a and 120 b fromconstituting a short circuit attributable to an electrode materialremaining at the recess of the contract hole 115.

As described above, according to the electrode substrate for a displaydevice according to each of the embodiments, it is possible to prevent ashort circuit of the adjacent pixel electrodes when forming the pixelelectrode without suffering the influence of the electrode materialremaining in the recess of the contact hole. In this way, it is possibleto reduce occurrence of defective pixels.

Therefore, it is possible to fabricate liquid crystal display devices athigh yields by applying the electrode substrates of the presentinvention to the array substrates in the liquid crystal display devices.

1. An electrode substrate for a display device comprising: a pluralityof scan lines and a plurality of signal lines which are disposed so asto intersect one another; a plurality of pixel electrodes disposed atrespective intersections; switching elements provided at the respectiveintersections, each of the switching elements being configured to allowconduction between the signal line and the pixel electrode by aninstruction of a gate signal to be supplied to the scan line and therebyto write a video signal supplied to the signal line into the pixelelectrode; a protection film formed between the signal line and thepixel electrode; and contact holes configured to connect the signal lineand one electrode of the switching element, wherein each of the signallines is formed so as to cover a gap between two pixel electrodes beingadjacent in a direction of the scan line, the contact holes causerecesses on the protection film, an end of only one of the two pixelelectrodes which are adjacent to each other while interposing the signalline is provided in a position extending into without extending beyondthe recess on the protection film caused by the contact hole, and an endof the other one of the two pixel electrodes is distant from an apertureedge of the contact hole by a longer dimension than a horizontaldimension of a tapered portion of the contact hole.